Nothing sucks worse than getting stranded out on the trail with a busted derailleur. Actually, we can think of some worse things, but it's still pretty bad. The Shimano Deore XT M773-SGS 10-speed Shadow rear derailleur though isn't going to leave you hanging. It's compatible with their 10-speed Dyna-Sys drive train, so it delivers smoother shifts, closer ratios so you'll have fewer dropped chains and a lot more riding....